This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Progression through the cell cycle is regulated at multiple checkpoints. For example, the spindle checkpoint monitors the fidelity of chromosome segregation. This checkpoint inhibits cells from progressing into anaphase until all sister chromatids are properly attached to the mitotic spindle and aligned at the metaphase plate. A number of proteins have been shown to be important in this process including MAD1, MAD2, TTK, Bub1, BubR1 and BubR2. To further understand the molecular mechanism by which these protein regulated the spindle checkpoint a mass spectrometry analysis was performed to identify phosphorylation sites on Mad1 by the TTK kinase.